This invention is related to a discharge tube lighting device which is preheated by a cathode, such as a fluorescent lamp.
There has been developed and produced both in this and other countries an electronic lighting device having a stabilizer circuit therein. The stabilizer circuit is superior to a conventional core-type inductor stabilizer with respect to power saving and quick lighting. However, a fatal breakdown of the fluorescent lamp and its stabilizer circuit may be caused as the lamp is worn out or blackened.
That is, the opposite filaments for emitting electrons in the lamp are worn out nonuniformly and the current within the lamp may have a diode property according to the degree of blackening of the lamp because the fluorescent lamp is a discharge tube preheated by a cathode. In particular, unexpected characteristics may appear according to the kind, mixing rate, or pressure of the gas used in the tube.
The electronic stabilizer circuit is of a high frequency switching type wherein the switching state may become abnormal according to the degree of the blackening of the lamp, which corresponds to the circuit load. In this case the breakdown of the stabilizer may be caused by overcurrent and overheating of the elements.
For preventing the breakdown of the stabilizer, a stabilizer protective circuit is required. A known stabilizer protective circuit has the disadvantage that it is opened when the elements are overheated and then automatically closed when the elements cool down.
With this known protective circuit, when the elements are overheated without lighting of the fluorescent lamp, the circuit is opened and in sequence, the elements cool down, thus causing closure of the circuit. This repetitive overheating of the elements--opening of the circuit--cooling down of the elements--closing of the circuit can continue indefinitely whereby the fluorescent lamp twinkles continually at cooling intervals.
Even with fluorescent lamps constructed in this manner, no big problem has arisen in location having a low ceiling since replacement of the lamp is easily achieved. However, in places having a high ceiling as, for example, in a plant or factory, the replacement of one or two disabled fluorescent lamps among many is not easy. If the disabled lamps are left as they are, the stabilizers are overloaded.